Process for the production of styrene and butadiene



e. A. NESTY ETAL 2,400,774 PROCESS FOR THE PRODUCTION OF STYRENE AND BUTADIENE May 21, 1946.

Filed NOV. 4, 1943 1 C 7 0 W 6 M C6 Con erlcr 5N TOR 675?)? iii 6553/ B 614% MzgyeZ/Eower ATTORNEY factory purit to meet the for. 4

It is an object of this invention to provide a new process for the rema n 21, 9 6 I UNITED STATES PATENT ,oI-Fics raoca' ss Foa THE-PRODUCTION F STYRENE AND BUTADIENE Glenn Albert Nesty, Syracuse, and V Christian Klingelhoefer, Baidwinsville, N. Y-

asslgnors to The Solvay York, N. Y.,

Process Company, New a corporation of New York Application November}, 1943, Serial No. 568,922 4 Claims. (Cl. 260669) This invention relates to the production of Styrene is at present obtained from a variety of sources. It may be manufactured synthetically by reacting benzene with ethylene to form ethyl benzene and then dehydrogenating' the ethylbenzene to produce styrene; while this process has been extensively employed, it has the disadvantages that two separate steps are involved. Styrene may also be obtained in the fractionation of coal tar or from'products formed during the cracking or reforming of petroleum distillates; however, neither of these sources is at present capable of supplying sufficient styrene of satispresent demand thereproduction of-styrene frombenzene and ethylene.

It is a more particular object of this invention to provide a one-step process whereby benzene and ethylene are reacted to form styrene, as well as appreciable quantities of butadiene.

I We have found that by carrying out the reac tion of benzene and ethylene under carefully controlled conditions as hereinafter specified so as to avoid undue attack on the reactants, styrene may be directly produced in one step in commercially valuable quantities and, in addition, that appreciable amounts 'ofbutadiene may also be recovered from the reaction mixture. The proc ass by which such advantageous results may be achieved involves reacting benzene and ethylene in the gaseous phase at a temperature between about 775 and about 850 0., and at a space velocity from about 75 to about 700 reciprocal hours, themol ratio of ethylene to benzene introduced into the reacton being such that an excess of ethylene is present preferably, such tween about 1.3 and about 2.3.

The process of our invention may be most advantageously carried out by a mixture of ethylene and benzene, the mol ratio of ethylene to benzene being between about 1.3 and about that the mol ratio of ethylene to benzene is betained at a temperature between 775 and '850 C.

at a space velocity between about 75 and about 700 reciprocal hours. In carrying out the reaction under the controlled conditions-above speci fled, not more than about 12% by volume of the benzene is attacked, of which between about 60% and about 75% by volume is converted to styrene;

under these conditions not more than about% by volume of the'ethylene introduced is attacked,

of which between about 15% and about byvolume is converted to styrene and between about 25% and about by volume to butadiene. After recovery of the styrene and butadiene products from the reaction mixture; the residual as containing hydrogenand unreacted ethylene v and the unreacted benzene may be returned to the reactor forthe production of further quantitles of styrene and butadiene.

From the above description it will appear our invention not only provides a method by which benzene and ethylenegmay be reacted to produce passed through the reactorstyrene in one, step I in commercially valuable quantities, but also permits simultaneous production of butadiene. In view of the fact an important type of synthetic rubber is manufactured from the primary reaction products of our invention, 1. e., butadiene and styrene, the processor "our invention, whereby simultaneous production of these ingredients is value.

The space velocity values given in the specificaefiected, is of obvious tion and claims are expressed, as is customary, in terms of the volume of vapors reduced to standard conditions of temperature and pressure per hour divided by the volume of the reactor.

k In carrying'out the process of our invention, a

' mixture of ethylene and benzene in which the mol l '2.3, at atmospheric pressure through a heated tube packed with crushed :flrebrick, and mainratio of ethylene to benzene is between about 1.3 and about 2.3, preferably about 2, is introduced into a-reactor which preferably is packed with crushed firebrick which, we have found, reduces the yield of undesirable by-products and thereby enhances the overall efliciency of the reaction, The ethylene employed need :not be absolutely pure but may contain as much as 10% by volume of inert. gases such as hydrogen. If desired,

steam may be incorporated in the mixture as adiluent. The temperature of the reactor should be between about 775 and a'bout'850" 0., a 'temperature of about 825 to 835 0. being preferred. The reacting gases'should be passed through the converter at space velocities of the order of to 700, preferably between about 400; and about 650 f reciprocal hours. The reaction is preferably carried out at atmospheric pressure since no ap- 5' preciable advantage is obtained, by using superor sub-atmospheric conditions, which, however, may

I be employed if desired.

- ditions it will j and about by volume of the benzene and between about8% and about by volume of the obtained bypassing.

above conbe found that-"between about 5% By operating in accordance with the ethylene'is attacked. Of the benzene attacked, between about 60% and about 75% by volume -is converted to styrene; of the ethylene attacked, between. about 15% and about 30% by volume is converted to styrene and between about 25% and about 40% by volume to butadlene.

The styrene may be recovered from the reaction gases by passing the gases through a scrubher in contact with asuitable styrene solvent.

Preferably the gases are scrubbed with benzene at a temperature between and 50 (3., the

' styrene and unreacted benzene being thus absorbed,

the styrene then recovered-by fractionae tion and the benzene either employed to react with furtherquantities of ethylene or returned to the scrubber; benzene contained in the gas leaving the scrubber may also be recovered if desired. The unabsorbed gases, which contain butadiene and unreacted ethylene. may then be scrubbed at a temperature between about 10" and about 30 C. with a further quantity of henzene in order to absorb the butadlene; the butadiene may be recovered by fractionation, andthe benzene returned. to the scrubber or employed for reaction with further quantities of ethylene. The gases passing. through the second scrubber,

' containing chiefly unreacted ethylene and hydrogen produced during the course of the reaction, maybe returned for further-reaction with ben-' zene after a portion thereof is bled trom the system to prevent undue build-up of the hydrogen concentration. I

In addition to styrene and butadlene, appreciable amount of biphenyl are also produced as well as other aromatic compounds such as naphthalene, disubstituted benzenes, substituted biphenyl, acenaphthylene and possibly anthracene. 3- and 4-carbon atom oleflns are formed from the ethylene under the conditions above specifled, although the amounts or theseconstituents are not large; theseproducts are usually recovered along with arated therefrom as desired. Acetylene is also f. produced in appreciable quantitie together with 7 smaller amounts of methane; these gases pass thebutadiene and may be sepmixture having a moi ratio of ethylene to benzene of about 2 is produced. This gaseous mixture is then passed to converter 2, which may appropriatelybe a reactor lined and packed with firebrick, maintained at a temperature in theneighborhood of 825 to 835 C., the gaseous mixture flowing through converter 2 at a space velocity between about 400 and about 650 reciprocal hours.

,The reaction mixture withdrawn from converter 2 is passed to scrubber 3 wherein the gaseous mixture is scrubbed with benzene at a temperature'of between about 20 and about 50 C., the styrene and unreacted benzene being thereby absorbed. The solution of styrene in benzene withdrawn from scrubber 3 is passed to fractionator 4 operated at a reduced pressure of approximately 0.2 atmosphere wherein the benzene is removed by distillation and return tovaporizer i. A styrene fraction covered from the still. The residue in the still containing biphenyl, naphthalene, anthracene oil, tar and carbon isdiscarded or fractionated -for recovery of biphenyl and naphthalene.

The unabsorbed gases from scrubber 3, containing butadlene and unreacted ethylene, are passed to scrubber 5 wherein they are scrubbed with a benzene solution maintained at a temperature between about 10 and about 30 C., the butadlene being thus absorbed; the solution oi butadiene in benzene removed from scrubber .5 also contains somed -carbon atom oleiins, as well as 2- and 3-carbon atom compounds, formed during the course of the reaction-and absorbed in the benzene. This soiution'is withdrawn from the base ,of scrubber 5 to fractionator 6 wherein the solution is distilled at a pressure of about 1 her 5 comprise chiefly the-unreacted ethylene,.

through the butadlene recovery step along with I hydrogen unreactedethylene and may be returned with the. unreacted ethylenefor further reaction with benzene without-appreciably arfecting7the course of the reaction as long as a portion of the gaseous mixture being thus recycled is bled irom the system in order to maintain the concentration or the gaseousby-product above mentioned relatively low.

We have surprisingly'tound that although butadiene is'. presumably ethylene without benzene entering'into the, reaction, the presence 01' yields of butadlene pure ethylene through the converte'runder the same conditions.

' A specific embodiment of our invention is illustrated diagrammatically in Figure 1. As shown in Figure 1 benzene andethylene together with fan" ethylene-hydrogen mixture recovered from the process as hereinafter described, are mixed in vaporizer I in proportionssuch that use; the remaining is returned to vaporizer produced, directly trom' benzene in the reaction mixture enhances production of. butadiene from ethyleneunderthe above conditions. since the obtained are greater-than are to 5 atmospheres, the butadlene being recovered in crude form admixed with some 3- and e-carbon atom compounds at apoint intermediate the length of th fractionating column. removed from the top of fractionator 8 are returned to scrubber 5 to recover any butadleneportion at the. benzene remaining therein. A residue from rractionator B is passed to cooler I and then returned to either scrubber 8 or scrubher 5; the remainder of the benzene'from fractionator 0 is returned to vaporiz r! for furt er reaction. I i

The unabsorbed gases withdrawn from scrubalthough appreciable amounts of hydrogen, acetqylene and methane are-also present. Approxb mately 20% by, volume of these gases is bled from the system and the ethylene contained in the bleed separated from the other gases for reof the unabsorbed gases I for further reaction with benzene. l

The .iollowing invention:

A sase example is illustrative of our through a silica tube'packed with 6-10 mesh 'crushed firebrick and maintained at a 'tempera-' ture or 825 0.; the volume or .the reaction zone in this tube was 11 cubic inches. Analysis of the f gases showed that approximately 7.9% by volume or the benzene and. 10.8% .by. volume or the ethylene were attacked. O! the benzene attacked-69.5% by volume was'converted to styrene;

25% by volume 0! the ethylene attacked was converted to styrene and 25.6% by volume was convapor u .verted to butadlene.

of purity is then re- The gases mixture or ethylene and benzene, the moi ratio or. ethylene to benzene being 2.04, was passed at a space velocity or 642 reciprocal hours .of styrene and butadiene which comprises passing a gaseous mixture of ethylene and benzene, the moi ratio or ethylene to benzene being between about 1.3 and about 2.3, through a reactor v maintained at a temperature between about 775 and about 850 C. at a space velocity or between about 75 and about '700 reciprocal hours, where- .by not more than about 12% by volume of the It will be evident from the above description that the process or our invention provides a new and about 15% by volume or the ethylene is at.-

tacked, and recovering styrene and 'butadiene from the resulting mixture.

' 3. A p'rocess for the simultaneous production of styrene and butadiene which comprises passing'a gaseous mixture of ethylene and benzene,

the moi ratio of ethylene to benzene being about 2, through a reactor packed with flrebrick and maintained at atemperature between about 825 and about 835 0. at a space velocity or between benzene and not more than by voiume'ot the ethylene is attacked, and recovering butadiene and styrene from the reaction mixture.

2. A process for the'simultaneous production of styrene and butadiene which comprises passing a gaseous mixture or ethylene and benzene.

. the moi ratio of ethylene .to benzene being about 2, through a. reactor packed with flrebrick and maintained at a temperature or between about 825 and about 835 C. at a space velocity 01 between about 400 andabout 650 reciprocal hours.

about 400 and about 650 reciprocal hours, contacting the reaction mixture with benzene at'a temperature between about 20 and about- 0. to remove styrene and unreacted benzene therefrom, recovering styrene from the benzene solution produced, contacting the gases which are not absorbed in the benzene with further quantities of benzene at a temperature between about 10 and about 30 C. to remove butadiene therefrom, recovering butadiene from the solution produced, and returning to the reactor ethylene containing gases which remain unabsorbed.

4. A process for the simultaneous production of styrene and butadiene which involves passing a a gaseous mixture of benzene and ethylene, the mol whereby between about 5% and about 10% by ratio of ethylene to benzene being such that an excess 01. ethylene is present, through a reactor at a temperature maintained between about 775 and 850-Q, at a space velocity between about '15 and 700 reciprocal hours.

GLENN ALBERT NEB'I'Y. WILLIAM CHRIB'I'IAN KLINGELHOEF'EB;

volume or the benzene and between about 8%. 

